Strength and shrinkage properties of alkali-activated slag concrete placedinto a large column

The properties of alkali-activated slag concrete (AASC) are generally deter mined on small-scale laboratory-produced prisms or cylinders. This investig ation reports the in situ strength and in situ strain results from measurem ents on an 800 X 800 X 1200-mm column composed of AASC produced at a concre te plant. The results are contrasted with those of columns made with ordina ry portland cement (OPC) and blended cement (50% OPC + 50% slag) designated as GB50/50. For this type of AASC, the workability improved from the time of production to the time of concrete placement and minimal slump loss occu rred over 2 hours (in contrast with OPC). The rate of in situ temperature d evelopment was similar to GB50/50, and slower than OPC; however, the maximu m temperature difference between the interior and the exterior was consider ably less than OPC and GB50/50, The in situ strength was identical to OPC a nd superior to GB50/50 at 28 and 91 days. Embedded strain gauges show small initial in situ expansion within the centre of the column followed by a ra pid rate of tensile strain growth up to 14 days. At 91 days the differentia l strain between the centre of the column and the corner was sufficient to crack OPC concrete; however, the AASC column remained uncracked. Possible e xplanations for this behaviour could be due to a greater tensile strain cap acity of AASC than OPC concrete caused by greater creep and lower elastic m odulus and higher tensile strength of AASC. (C) 1999 Elsevier Science Ltd. All rights reserved.